Fluid Domain disappears in cycles viewport render
Solution - to bring Fluid Domain whole visible in a viewport:


under Render Properties > Performance > Dynamic BVH change to Static BVH






or under Object Data Properties > Normals enable Auto Smooth





I don't have an explanation for that, very precise pixel based cut looks like some kind of clipping, but I don't see any type active. Also I was thinking about some flipped normals that caused something similar to me once (that's why auto-smooth probably worked here), but since the cliping is straight, it can't be a faces of fluid sim rather than something that cross it, but there is nothing like that ... :) Did you used FlipFluid add-on for that?

So, mystery wasn't explained yet :) But probably future generations will find some useful string of meanings from my notes, that brings a light into this dark old 2.79x ... :)

Anyway I don't have this issue in 2.8x